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30 Dec 2002

Volume 81, Issue 27, pp. 5099-5257

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Bulk and surface contributions to resonant second-harmonic generation from Si(001) surfaces

Yong Qiang An and Steven T. Cundiff

Appl. Phys. Lett. 81, 5174 (2002); http://dx.doi.org/10.1063/1.1533122 (3 pages) | Cited 10 times

Online Publication Date: 19 December 2002

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The spectra of the isotropic and anisotropic contributions to second-harmonic generation from modified Si(001) surfaces are separated using polarization selection and rotational anisotropy. A bulk anisotropic resonance is observed at a two-photon energy of 3.42±0.01 eV. The isotropic surface contributions for native oxide Si and thermal oxide Si show peaks at 3.39±0.01 eV and 3.35±0.01 eV, respectively. Interference between these contributions and the bulk signal can shift the apparent resonance position if they are not separated. The surface produces a noninterfering contribution that is comparable to the interfering contribution for H-terminated Si but negligible for oxidized silicon. © 2002 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.20.Ek Optical activity
81.65.Mq Oxidation

Growth of Au-catalyzed ordered GaAs nanowire arrays by molecular-beam epitaxy

Z. H. Wu, X. Y. Mei, D. Kim, M. Blumin, and H. E. Ruda

Appl. Phys. Lett. 81, 5177 (2002); http://dx.doi.org/10.1063/1.1532772 (3 pages) | Cited 55 times

Online Publication Date: 19 December 2002

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Ordered gallium arsenide (GaAs) nanowires are grown by molecular-beam epitaxy on GaAs (111)B substrates using Au-catalyzed vapor–liquid–solid growth defined by nanochannel alumina (NCA) templates. Field-emission scanning electron microscope images show highly ordered nanowires with a growth direction perpendicular to the substrate. The size (i.e., diameter) distribution of the wires is drastically narrowed by depositing the gold catalyst through an NCA template mask; this narrows the size distribution of the gold dots and arranges them in a well-ordered array, as defined by the NCA template. The nanowire diameter distribution full width at half maximum on the masked substrate is 5.1 nm, compared with 15.7 nm on an unmasked substrate. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.Hc Catalytic methods
61.46.-w Structure of nanoscale materials
81.05.Ea III-V semiconductors
81.07.Vb Quantum wires

Kinetics of electric-field-enhanced crystallization of amorphous silicon in contact with Ni catalyst

Hae-Yeol Kim, Binn Kim, Jong-Uk Bae, Kwang-Jo Hwang, Hyun-Sik Seo, and Chang-Dong Kim

Appl. Phys. Lett. 81, 5180 (2002); http://dx.doi.org/10.1063/1.1532533 (3 pages) | Cited 6 times

Online Publication Date: 19 December 2002

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Electric-field-enhanced crystallization of hydrogenated amorphous silicon in contact with nickel catalyst (Ni/a-Si:H) has been investigated. In order to elucidate the crystallization kinetics quantitatively, in situ conductivity measurement was used. With the change of Ni dose (4×1013 ∼ 1.3×1015 cm−2) and annealing temperature (550 ∼ 500 °C), crystallization rate varied drastically at the electric field of 33 V cm−1. The activation energy for the crystallization was found to be strongly dependent on the Ni dose, 85 kJ mol−1 for 1.3×1015 Ni cm−2, 243 kJ mol−1 for 6×1014 Ni cm−2, and 276 kJ mol−1 for 4×1013 Ni cm−2, respectively. The polycrystalline silicon films were composed of needle-like crystallites of ∼ 5 μm (long axis) and their thin-film transistors (TFTs) showed field effect mobility of 43 cm2 V−1 s−1. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.43.Dq Amorphous semiconductors, metals, and alloys
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.30.Tv Field effect devices
73.61.Cw Elemental semiconductors

Surface band bending, nitrogen-vacancy-related defects, and 2.8-eV photoluminescence band of (NH4)2Sx-treated p-GaN

Yow-Jon Lin, Zhi-Long Wang, and Hsing-Cheng Chang

Appl. Phys. Lett. 81, 5183 (2002); http://dx.doi.org/10.1063/1.1533857 (3 pages) | Cited 10 times

Online Publication Date: 19 December 2002

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We have employed the photoluminescence and x-ray photoelectron spectroscopy measurements to study the effects of (NH4)2Sx treatment on the p-type GaN (p-GaN). After (NH4)2Sx treatment, we found that the reduction of the surface state, related to nitrogen-vacancy defects on the p-GaN surface, led to a reduction in surface band bending by 0.25 eV. The surface band bending reduction and surface state reduction caused by the (NH4)2Sx surface treatment could be useful for the formation of ohmic and Schottky contacts between the metal and p-GaN layers. In addition, the intensity of the 2.8-eV photoluminescence band depended on the amount of nitrogen vacancy of p-GaN, which was also investigated in this study. © 2002 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
73.20.At Surface states, band structure, electron density of states
68.35.Dv Composition, segregation; defects and impurities
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Characteristics of silicon nanocrystal floating gate memory using amorphous carbon/SiO2 tunnel barrier

Seung Jae Baik and Koeng Su Lim

Appl. Phys. Lett. 81, 5186 (2002); http://dx.doi.org/10.1063/1.1533119 (3 pages) | Cited 10 times

Online Publication Date: 19 December 2002

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Nanocrystal floating gate memory employing an amorphous carbon (a-C)/SiO2 double-layered tunnel barrier was fabricated. The band gap of a-C and conduction band discontinuity between a-C and Si was estimated to be 1.95 and 0.4 eV, respectively. In addition, interface states density of the a-C/SiO2/channel Si was estimated from the capacitance–voltage measurement. The nanocrystal memory using this tunnel barrier exhibited enhanced charge retention than that employing a single SiO2 tunnel barrier whereas the injection efficiency is comparable between them, which is due to the asymmetrical band profile of the tunnel barrier. © 2002 American Institute of Physics.
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84.30.Sk Pulse and digital circuits
85.35.-p Nanoelectronic devices

Experimental observation of electron velocity overshoot in AlN

R. Collazo, R. Schlesser, and Z. Sitar

Appl. Phys. Lett. 81, 5189 (2002); http://dx.doi.org/10.1063/1.1534407 (3 pages) | Cited 5 times

Online Publication Date: 19 December 2002

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The energy distribution of electrons transported through intrinsic AlN heteroepitaxial films grown on 6H-SiC was directly measured as a function of the applied electric field. Following the transport, electrons were extracted into vacuum through a semitransparent Au electrode and their energy distribution was measured using an electron spectrometer. Transport through 80-nm-thick layers indicated the onset of quasiballistic transport for fields greater than 510 kV/cm. This was evidenced by a symmetric energy distribution centered at energies above the conduction band minimum. Drifted Fermi–Dirac energy distribution was fitted to the measured energy distribution, with the energy scale referenced to the bottom of the AlN conduction band. The drift energy and the carrier temperature were obtained as fitting parameters. Overshoots as high as five times the saturation velocity were observed and a transient length of less than 80 nm was deduced. In addition, the velocity-field characteristic was derived from these observations. © 2002 American Institute of Physics.
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73.50.Fq High-field and nonlinear effects
73.61.Ey III-V semiconductors
72.20.Ht High-field and nonlinear effects

Si doping of high-Al-mole fraction AlxGa1−xN alloys with rf plasma-induced molecular-beam-epitaxy

Jeonghyun Hwang, William J. Schaff, Lester F. Eastman, Shawn T. Bradley, Leonard J. Brillson, David C. Look, J. Wu, Wladek Walukiewicz, Madalina Furis, and Alexander N. Cartwright

Appl. Phys. Lett. 81, 5192 (2002); http://dx.doi.org/10.1063/1.1534395 (3 pages) | Cited 10 times

Online Publication Date: 19 December 2002

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Very high levels of n-type doping of AlxGa1−xN alloys were recently achieved by rf plasma-induced molecular-beam epitaxy on sapphire substrates and Si as a dopant. Electron concentrations were obtained up to 1.25×1020 cm−3 when the Al mole fraction was 50%, and 8.5×1019 cm−3 electrons were measured even when the Al mole fraction was 80%. Other material properties were determined by optical absorption, photoluminescence, cathodoluminescence, x-ray diffraction, and atomic force microscopy measurements and high optical and morphological qualities were shown. © 2002 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Kinetic roughening study of perylene on glass and Au substrates

Serkan Zorba, Li Yan, Neil J. Watkins, and Yongli Gao

Appl. Phys. Lett. 81, 5195 (2002); http://dx.doi.org/10.1063/1.1534416 (3 pages) | Cited 3 times

Online Publication Date: 19 December 2002

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We have investigated the growth kinetics of perylene, an organic semiconductor with high carrier mobility, on glass and Au substrates grown side-by-side by vapor deposition using atomic force microscopy. Our results show that kinetic roughening theory can reveal a wealth of information about polycrystalline growth. Higher order height–height correlation functions have been calculated for the perylene thin films on glass and Au. These results show that the height–height correlation function and the Hurst exponent saturate once the nominal perylene film thickness reaches the critical value of 40 Å on glass, and 100 Å on Au. After these thicknesses, overhang structures develop and dynamic scaling analysis becomes inappropriate. In addition, we have observed a complex, multiaffine behavior on both substrates evidenced by order dependence of the Hurst exponent. Grain size distribution and shape analysis were also performed on our films. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Ps Atomic force microscopy (AFM)
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Improved corrosion resistance of IrMn by Cr and Ru additions

M. J. Carey, A. Kellock, L. Baril, J. R. Childress, T. Le, T. Thompson, and B. A. Gurney

Appl. Phys. Lett. 81, 5198 (2002); http://dx.doi.org/10.1063/1.1526910 (3 pages) | Cited 7 times

Online Publication Date: 19 December 2002

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The magnetic and corrosion properties of Ir16Mn84 with Ru and Cr additions have been studied. Spin valves with Ir16Mn84–Ru have slightly lower Hex and Tb than when pure Ir16Mn84 is used. The corrosion properties improve, Hex and Tb improve with 3 vol % Cr, but drop considerably with more Cr additions, losing 21% of the pure IrMn value by 12 vol % Cr. The corrosion current and potential are Ic = 8 μA/cm2 and E0 = −580 mV respectively, for Ir16Mn84 with 12 vol % Cr. This represents a significant improvement over pure Ir16Mn84, which has Ic = 100 μA/cm2 and E0 = −1300 mV. When Ru is used as the additive, Ic and E0 are 10 μA/cm2 and −100 mV, respectively, for 9 vol %. Cr is the superior additive, especially in small concentrations where it shows a significant decrease in the Ic without degrading the magnetic properties. © 2002 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics

Magnetic and martensitic phase transitions in ferromagnetic Ni–Ga–Fe shape memory alloys

K. Oikawa, T. Ota, T. Ohmori, Y. Tanaka, H. Morito, A. Fujita, R. Kainuma, K. Fukamichi, and K. Ishida

Appl. Phys. Lett. 81, 5201 (2002); http://dx.doi.org/10.1063/1.1532105 (3 pages) | Cited 149 times

Online Publication Date: 19 December 2002

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Ferromagnetic shape memory alloys with a body-centered-cubic ordered structure in a Ni–Ga–Fe system have been developed. The alloys with the composition range of Ni 27 at. % Ga (20–22 at. %)Fe exhibit a thermoelastic martensitic transformation from a B2 and/or an L21 parent to a martensite phase, with a seven-layer modulated (14M) and a five-layer modulated (10M) structure, in the ferromagnetic state. The parent phase transforms from the B2 to the L21 structure at about 970 K during cooling, and the degree of the L21 order in the parent phase is increased by annealing at 773 K, resulting in the increase of both the martensite starting and the Curie temperatures. The ductility of these alloys is improved by introducing of a small amount of a γ-phase solid solution. Consequently, we can conclude that the present alloys are promising for ferromagnetic shape memory alloys. © 2002 American Institute of Physics.
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81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys
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Thickness of the near-interface regions and central bulk ohmic resistivity in lead lanthanum zirconate titanate ferroelectric thin films

D. P. Chu, Z. G. Zhang, P. Migliorato, B. M. McGregor, K. Ohashi, K. Hasegawa, and T. Shimoda

Appl. Phys. Lett. 81, 5204 (2002); http://dx.doi.org/10.1063/1.1532548 (3 pages) | Cited 9 times

Online Publication Date: 19 December 2002

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We have developed a method to separate the low-resistive near-interface regions (NIRs) from the high-resistive central bulk region (CBR) in a ferroelectric thin film. The NIR thickness and the CBR resistivity can thus be accurately determined. Using lanthanum-doped lead zirconate titanate films as an example, we show that the total thickness of the NIRs depends only on the electrode materials in use (Ir and Pt), while the CBR resistivity depends only on the impurity doping levels (La = 1.5% and 3%). The fact that the NIR is much narrower when Pt electrodes are used instead of Ir, and that the NIR resistivity is always considerably lower than the central bulk, suggest that the NIRs is probably originated from material nonstoichiometry/defects rather than the band bending at metal/insulator interfaces. © 2002 American Institute of Physics.
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85.50.Gk Non-volatile ferroelectric memories
77.55.-g Dielectric thin films
73.40.Rw Metal-insulator-metal structures
77.80.-e Ferroelectricity and antiferroelectricity

Study of ferroelectricity and current–voltage characteristics of CdZnTe

D. J. Fu, J. C. Lee, S. W. Choi, S. J. Lee, T. W. Kang, M. S. Jang, H. I. Lee, and Y. D. Woo

Appl. Phys. Lett. 81, 5207 (2002); http://dx.doi.org/10.1063/1.1530744 (3 pages) | Cited 16 times

Online Publication Date: 19 December 2002

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CdZnTe has been characterized by means of polarization-field hysteresis and current–voltage measurements. The CdZnTe is shown to be ferroelectric with polarization endurance up to 107 poling cycles. The polarization is significantly influenced by free carriers and can be switched by light illumination. The capacitance of CdZnTe consists of ferroelectric and depletion components. On the other hand, electrical conduction in the CdZnTe is modulated by the polarization, leading to hysteresis in the current–voltage characteristics. Writing and reading measurement has shown a reading-current difference of 0.015 mA at a nondestructive voltage for the binary digits. © 2002 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
72.20.Fr Low-field transport and mobility; piezoresistance
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
81.05.Dz II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena

Mitigation of transverse domain growth in two-dimensional polarization switching of lithium niobate

L.-H. Peng, Y.-C. Shih, S.-M. Tsan, and C.-C. Hsu

Appl. Phys. Lett. 81, 5210 (2002); http://dx.doi.org/10.1063/1.1533115 (3 pages) | Cited 8 times

Online Publication Date: 19 December 2002

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This letter reports a charge control mechanism to mitigate the growth of transverse domain in the two-dimensional periodical polarization switching of Z-cut congruent-grown lithium niobate. This mechanism is established in a two-step procedure consisting of a first high temperature treatment followed by pulsed field poling. The ferroelectric χ(2) nonlinear photonic crystal thus formed exhibits a domain size as small as 3.3 μm and can emit an array of second harmonic green lasers when pumped by a Nd:yttritium–aluminum–garnet laser. These observations are ascribed to the (i) selective 180° domain nucleation underneath the oxidized electrode, and (ii) confinement of transverse domain motion to the positively charged boundary formed by the heat treatment. © 2002 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
42.70.Qs Photonic bandgap materials
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All-optical single-electron read-out devices based on GaN quantum dots

Irene D’Amico and Fausto Fossi

Appl. Phys. Lett. 81, 5213 (2002); http://dx.doi.org/10.1063/1.1532546 (3 pages) | Cited 16 times

Online Publication Date: 19 December 2002

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We study few-particle interactions in GaN-coupled quantum dots and discuss how the built-in field characteristic of these structures strongly reinforce dipole–dipole and dipole–monopole interactions. We introduce a semi-analytical model that allows for a rapid and easy estimate of the magnitude of few-particle interactions and whose predictions are closer than 10% to “exact” results. We apply our study to the design of an all-optical read-out device that exploits long-range dipole–monopole interactions and may be also used to monitor the charge status of a quantum dot system. © 2002 American Institute of Physics.
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85.35.Gv Single electron devices
73.63.Kv Quantum dots
78.67.Hc Quantum dots
85.60.-q Optoelectronic devices

Plasma deposition of Ultrathin polymer films on carbon nanotubes

Donglu Shi, Jie Lian, Peng He, L. M. Wang, Wim J. van Ooij, Mark Schulz, Yijun Liu, and David B. Mast

Appl. Phys. Lett. 81, 5216 (2002); http://dx.doi.org/10.1063/1.1527702 (3 pages) | Cited 39 times

Online Publication Date: 19 December 2002

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Ultrathin films of pyrrole were deposited on the surfaces of carbon nanotubes using a plasma polymerization treatment. High-resolution electron transmission microscopy images revealed that an extremely thin film of the polymer layer (2 ∼ 7 nm) was uniformly deposited on the outer and inner surfaces of the nanotubes. The nanotubes of all sizes exhibited equally uniform ultrathin films, indicating well-dispersed nanotubes in the fluidized bed reactor during the plasma treatment. In particular, the inner wall of the nanotube was also coated with a uniform ultrathin film of only ∼1–3 nm. Time-of-flight secondary ion mass spectroscopy experiments confirmed the highly branched and cross-linked polymer thin films on the carbon nanotubes. The plasma deposition mechanism is discussed in this letter. © 2002 American Institute of Physics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
52.77.Dq Plasma-based ion implantation and deposition
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.07.De Nanotubes
82.35.Gh Polymers on surfaces; adhesion

Tip-gating effect in scanning impedance microscopy of nanoelectronic devices

Sergei V. Kalinin, Dawn A. Bonnell, Marcus Freitag, and A. T. Johnson

Appl. Phys. Lett. 81, 5219 (2002); http://dx.doi.org/10.1063/1.1531833 (3 pages) | Cited 14 times

Online Publication Date: 19 December 2002

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Electronic transport in semiconducting single-walled carbon nanotubes is studied by combined scanning gate microscopy and scanning impedance microscopy (SIM). Depending on the probe potential, SIM can be performed in both invasive and noninvasive modes. High-resolution imaging of the defects is achieved when the probe acts as a local gate and simultaneously as an electrostatic probe of local potential. A class of weak defects becomes observable even if they are located in the vicinity of strong defects. The imaging mechanism of tip-gating scanning impedance microscopy is discussed. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
85.35.Kt Nanotube devices
07.79.-v Scanning probe microscopes and components

Annealing-induced reversible change in optical absorption of Ag nanoparticles

Huijuan Bi, Weiping Cai, Lide Zhang, D. Martin, and F. Träger

Appl. Phys. Lett. 81, 5222 (2002); http://dx.doi.org/10.1063/1.1532757 (3 pages) | Cited 16 times

Online Publication Date: 19 December 2002

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Optical absorption of silver nanoparticles dispersed within pores of monolithic mesoporous silica was investigated after annealing in different atmospheres. It has been found that treatment in H2 or N2 induces a strong surface plasmon resonance (SPR) as usually expected, but air annealing results in the disappearance of the SPR, which is contrary to the fact that bulk metal silver is stable and not oxidized in air at above 200 °C. The absence and appearance of the SPR absorption can be controlled through alternate annealing in air and H2 (or N2). Thermodynamic analysis for oxidation of Ag nanoparticles, by additionally considering the surface and curvature effects of a particle, shows the existence of critical particle size. Only when a Ag particle size is smaller than the critical value is the oxidation possible in air at above 200 °C. The optical changes are attributed to the occurrence of the redox of the Ag particles in different atmospheres at a high temperature. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.40.Kc Metals, semimetals, and alloys

Synthesis of boron nitride nanofibers and measurement of their hydrogen uptake capacity

Renzhi Ma, Yoshio Bando, Tadao Sato, Dmitri Golberg, Hongwei Zhu, Cailu Xu, and Dehai Wu

Appl. Phys. Lett. 81, 5225 (2002); http://dx.doi.org/10.1063/1.1534415 (3 pages) | Cited 18 times

Online Publication Date: 19 December 2002

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High-purity boron nitride (BN) nanofibers with diameters ranging from 30 to 100 nm were synthesized. Electron energy loss spectroscopy revealed that they have stoichiometric BN composition. The hydrogen uptake capacity measurements showed that the fibers could adsorb 2.9 wt % hydrogen under ∼10 MPa at room temperature. This hydrogen uptake capacity was compared with those of BN multiwalled or bamboo-like nanotubes under the same experimental conditions. It was suggested that the unique morphology of nanofibers, namely open-ended BN edge layers on the exterior surface, might facilitate hydrogen adsorption. © 2002 American Institute of Physics.
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84.60.Ve Energy storage systems, including capacitor banks
61.46.-w Structure of nanoscale materials
81.40.Vw Pressure treatment
68.43.Mn Adsorption kinetics
79.20.Uv Electron energy loss spectroscopy
81.07.Bc Nanocrystalline materials
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
62.50.-p High-pressure effects in solids and liquids

Electronic structure and interband transitions of metallic carbon nanotubes

P. N. D’yachkov, H. Hermann, and D. V. Kirin

Appl. Phys. Lett. 81, 5228 (2002); http://dx.doi.org/10.1063/1.1533858 (3 pages) | Cited 18 times

Online Publication Date: 19 December 2002

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Band structure of the metallic (n,n) carbon nanotubes (coefficients n are the indices of the two-dimensional primitive lattice vectors of the graphene lattice) is calculated in terms of a linear augmented cylindrical wave method. The results are used to correlate the minimum direct energy gaps E11 between the conduction and valence band singularities with the nanotube diameter d and optical absorption spectra. Significant deviations from the equation E11 ∼ d−1 are observed. The ππ∗ gap energy increases monotonically with 1/d, whereas the σπ∗ gap width shows a minimum at n = 10. In the (3, 3) tube, the conduction band singularity coincides with the Fermi level, resulting in a drastic increase of the density of states on this level. © 2002 American Institute of Physics.
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73.22.Dj Single particle states
78.67.Ch Nanotubes

Piezoresponse force microscopy of lead titanate nanograins possibly reaching the limit of ferroelectricity

A. Roelofs, T. Schneller, K. Szot, and R. Waser

Appl. Phys. Lett. 81, 5231 (2002); http://dx.doi.org/10.1063/1.1534412 (3 pages) | Cited 79 times

Online Publication Date: 19 December 2002

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Single ferroelectric lead titanate (PTO) grains down to 15 nm were fabricated by chemical solution deposition. Varying the dilution of the precursor solution leads to different grain sizes between 15 and 200 nm. The grain-size-dependent domain configuration was studied using three-dimensional piezoresponse force microscopy (PFM). It is found that the PTO grains in a dense film contain laminar 90° domain walls, whereas separated PTO grains show more complicated structures of mainly 180° domain walls. For grains smaller than 20 nm, no piezoresponse was observed and we suppose this could be due to the transition from the ferroelectric to the superparaelectric phase which has no spontaneous polarization. Recent calculations showed that the ferroelectricity of fine ferroelectric particles decrease with decreasing particle size. From these experiments the extrapolated critical size of PTO particles was found to be around 4–14 nm. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.-a Thin film structure and morphology

Intrinsic electron transport properties of carbon nanotube Y-junctions

Vincent Meunier, Marco Buongiorno Nardelli, J. Bernholc, Thomas Zacharia, and Jean-Christophe Charlier

Appl. Phys. Lett. 81, 5234 (2002); http://dx.doi.org/10.1063/1.1533842 (3 pages) | Cited 37 times

Online Publication Date: 19 December 2002

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The electron transport properties of three-terminal carbon-nanotube junctions are investigated within the Landauer theory of quantum conductance. Using a realistic tight-binding Hamiltonian, we demonstrate that the experimentally observed rectifying behavior is not an intrinsic property of the junction, but rather of the contact geometry. When semiconducting nanotubes are connected to metallic leads, nontransmitting states are induced at the nanotube–metal interface, leading to asymmetric transmission curves and potentially rectifying behavior of the nanodevice. © 2002 American Institute of Physics.
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73.63.Fg Nanotubes
73.40.Ei Rectification
73.40.Ns Metal-nonmetal contacts

A glow-discharge approach for functionalization of carbon nanotubes

Bishun N. Khare, M. Meyyappan, Joel Kralj, Patrick Wilhite, Metagus Sisay, Hiroshi Imanaka, Jessica Koehne, and Charles W. Baushchlicher

Appl. Phys. Lett. 81, 5237 (2002); http://dx.doi.org/10.1063/1.1533859 (3 pages) | Cited 31 times

Online Publication Date: 19 December 2002

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We demonstrate the functionalization of single-walled carbon nanotubes (SWNTs) using a glow discharge for generating atomic or molecular radicals. A 30-s exposure to a cold plasma of H2 results in near-saturation coverage of SWNT with atomic hydrogen. Functionalization of SWNTs with atomic hydrogen is confirmed by an infrared band at 2924 cm−1, characteristic of C–H stretching mode. A corresponding decrease in the ultraviolet absorption is also observed, which is due to a loss of some conjugated C–C π bonds in hydrogen covered SWNTs. © 2002 American Institute of Physics.
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68.43.Pq Adsorbate vibrations
78.30.Na Fullerenes and related materials
78.40.Ri Fullerenes and related materials
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Acoustic barriers based on periodic arrays of scatterers

Juan V. Sanchez-Perez, Constanza Rubio, Rosa Martinez-Sala, Rafael Sanchez-Grandia, and Vicente Gomez

Appl. Phys. Lett. 81, 5240 (2002); http://dx.doi.org/10.1063/1.1533112 (3 pages) | Cited 30 times

Online Publication Date: 19 December 2002

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It is well known that certain periodic structures built by repetition of elements produce sound attenuation effects as a consequence of the destructive interference of the scattered waves by these elements. The sound attenuation results that we got from transmission experiments with these kind of structures, so-called sonic crystals (SCs), led us to think that SCs could be used as an acoustic barrier. Until now, most of the transmission experiments with these periodic arrays of scatterers have been performed under controlled conditions, so how they would behave outdoors is still not well known. In this letter we present outdoor-experimental results for two-dimensional SCs and from these it can be concluded that periodic arrays of scatterers are a suitable device to reduce noise in free-field conditions. © 2002 American Institute of Physics.
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43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles

In-fiber nematic liquid crystal optical modulator based on in-plane switching with microsecond response time

Bharat R. Acharya, K. W. Baldwin, R. A. MacHarrie, John A. Rogers, C. C. Huang, and R. Pindak

Appl. Phys. Lett. 81, 5243 (2002); http://dx.doi.org/10.1063/1.1532532 (3 pages) | Cited 16 times

Online Publication Date: 19 December 2002

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We describe a simple method and device design that enables fast in-plane electro-optic modulation in conventional nematic liquid crystal (NLC) devices. When combined with optimized NLC materials, this approach yields rotational speeds of 1°/μs (independent of rotation angle, over a wide range) at a moderately low voltage. The observed rotational dynamics indicate that even these high speeds may not represent fundamental physical limits. We demonstrate these ideas in a compact tunable NLC waveplate that uses microelectrodes patterned directly on the tips of optical fibers. These devices offer fast, continuously tunable optic axis with low insertion loss and good performance in the near infrared. Modulators that use this design have promising potential applications for polarization control and analysis in optical communication systems. © 2002 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
42.79.Hp Optical processors, correlators, and modulators

Design of semiconductor-waveguide-type optical isolators using the nonreciprocal loss/gain in the magneto-optical waveguides having MnAs nanoclusters

H. Shimizu and M. Tanaka

Appl. Phys. Lett. 81, 5246 (2002); http://dx.doi.org/10.1063/1.1533114 (3 pages) | Cited 14 times

Online Publication Date: 19 December 2002

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We have theoretically analyzed semiconductor-waveguide-type optical isolators, which are based on the nonreciprocal loss/gain in the magneto-optical waveguide having MnAs nanoclusters embedded in an InAlAs matrix. The whole device structure is grown on an InP substrate and the operation wavelength is 1.55 μm. In the TM mode, more than 119 dB/cm of isolation is predicted and the optimum device structure is discussed. Furthermore, we proposed and theoretically analyzed a semiconductor-waveguide-type optical isolator for the TE mode, which can realize 36 dB/cm of isolation. Since our waveguide-type optical isolators are composed of all semiconductor-based materials, they can be easily integrated with III–V based optoelectronic devices such as edge-emitting laser diodes. © 2002 American Institute of Physics.
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85.70.Sq Magnetooptical devices
42.82.Et Waveguides, couplers, and arrays
42.82.Bq Design and performance testing of integrated-optical systems
42.15.Eq Optical system design
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